Physiological and enhanced physiological tremor

Abstract

Physiological tremor, sensu strictu, is an inevitable consequence of muscle contraction. Although it is roughly an order of magnitude larger than ballisto-cardiograph tremor (passive vibrations of body parts due to the periodic force perturbations produced by contraction of the heart with ejection of blood against the arch of the aorta, etc.), physiological tremor nevertheless is difficult to see with the naked eye. Its demonstration requires either optical magnification (such as provided by a dissecting or operating microscope) or a mechanical-to-electrical transducer of some type with subsequent electronic amplification. Tremor movements can be studied directly by using a goniometer, the arms of which, attached to a potentiometer, are carefully applied to the body part being studied, with the axis of the potentiometer positioned precisely coaxial with the joint to be studied. Either velocity and acceleration of tremor movements can be derived electronically from changes in position or acceleration can be measured directly by attaching a sensitive piezoelectric accelerometer to the moving part. Although positioning this latter transducer is less critical than when one uses a goniometer, care must nevertheless be taken to arrange that the acceleration being recorded is due only to movement at the joint under consideration-with an accelerometer on the dorsum of the hand, if the arm is held outstretched, a complex acceleration recording is then made which is due to summation of acceleration produced at all joints of the limb and by movements of the trunk itself.

Supported in part by the Parkinson’s Disease Fund of the Massachusetts General Hospital.